Earth, distance, expected period?

Question

A space laboratory is in circular orbit around the Earth at a distance of 6000km from the Earth's centre; it's period is 2hr 12min. An orbital telescope is to be placed into orbit at 12,000km. What is the expected period and which is the appropriate law upon which this is based? i have done calculations on this but i'm not sure they are right which is why i want some opinions! cheers xx

Answer 1

I'm not sure where you got this question from, but if it was orbiting at 6000 km from the centre of the Earth, it would be about 400 km underground.

Answer 2

Hmm - ingoring the problem of the distance compared to the radius of the earth....

You need to apply Kepler's 3rd law.

period squared is proportional to radius of orbit cubed.

Since you have the period and radius of orbit for one object you can calculate the constant of proportionality and then figure out the period of the telescope from its orbital radius.